The role of phosphorylation in the regulation and maintenance of protein synthesis will be examined. Emphasis will be placed on the site-specific phosphorylation of initiation factor 2 (eIF-2), ribosomes and aminoacyl-tRNA synthetases. eIF-2, phosphorylated at 4 different sites by 3 different protein kinases, and 40S ribosomal subunits, phosphorylated at 4-5 sites on protein S6 by 3 different protein kinases and at 1 site on protein S10 by another protein kinase, will be examined in a reconstituted protein synthesizing system and in the various partial reactions of protein synthesis. We will examine the hemin requirement for maintenance of protein synthesis in reticulocytes using a hemin-affinity column to isolate the hemin-binding proteins. The aminoacyl-tRNA synthetases which are regulated by phosphorylation will be identified. Several enzymes of interest, including methionyl-tRNA synthetase, will be purified. These aminoacyl-tRNA synthetases will be examined at the molecular level to determine the role of phosphorylation in the regulation of activity.